Thread: Knifemaking photo-essay (2)

The previous post in this series was: https://www.nzhuntingandshooting.co....ay-1-a-104989/

Heat treating.

I don’t have any images showing the heat treating process, however, I’ll describe what I do and show the gear I use.

1) With the furnace at 840°C, insert the knife blanks edge uppermost in a steel rack. By using a rack the blanks heat as evenly as possible – uneven heating can cause the blanks to warp.

2) A pair of scissor-handled heat treating pliers I put together more than 20 years ago.

3) Imagine the tray is 4/5 full of used engine oil. The blank has been in the furnace at 840°C for at least 10 minutes. I dip the red-hot blank edge-first into the oil and move it up and down to cool it as quickly as possible. (DON’T move the hot blank from side to side in the oil – such movement can cause it to warp.)

4) When the blank has cooled sufficiently to be barely touchable, I wipe it down with a rag, and put it edge-up into a benchtop fan oven set at 150°C – the pink arrow indicates the blank. Note also the thermocouple probe sticking out from the top of the oven.

I usually harden a dozen or more blanks at a time. Once the hardened blanks are all in the 150°C oven, I bring the temperature up to 220°C, and temper them for an hour. Then I let the blanks cool to room temperature, put them in the freezer for two hours, bring them back to room temp., and temper for another hour at 220°C. With this heat treatment protocol, my hardness tester usually shows the blades range in hardness from 57 to 59 (Rockwell C scale).